I just started learning Esperanto on Duolingo and it's been a breeze. I've studied other European languages (Spanish, French, German, Latin) as a hobby before and Esperanto is kind of a streamlined hybrid of all those.

Interligua may be "more useful" as an auxlang but the size and history of the Esperanto community appeals to me.

I'm also studying Bahasa Indonesia right now; it also has a very regular and simple grammar. It's said to be the easiest non-European language for European language speakers to learn.